Sources of the Arctic Flora: Origins of Arctic Species inRanunculusand Related Genera

The arctic biome is a relatively young ecosystem with ∼2300 species of vascular plants. We studied the genusRanunculusas an example of the origin and evolution of the arctic flora. For this purpose we used molecular phylogenetic and clock analyses based on evaluation of nuclear ITS and chloroplastmatK‐trnK DNA sequences in 194 taxa ofRanunculusand closely related genera. Taxa occurring in the Arctic arose from seven phylogenetic lineages ofRanunculusand also in the generaCoptidiumandHalerpestes. Two clades ofRanunculusare species‐rich in the Arctic, i.e.,Ranunculussect.RanunculusandR. sect.Auricomus(both fromR. subg.Ranunculus), but this is due to a number of arctic “microtaxa” morphologically barely separate fromR. acrisin the former clade and the widely agamospermic species complex ofR. auricomusin the latter. Lineages with species adapted to wetlands or aquatic habitats are significant groups represented in the arctic flora (R. subg.Ranunculussectt.FlammulaandHecatonia/Xanthobatrachium,R. subg.Batrachium, genusCoptidium) but show no clear signs of radiation in the Arctic or the northern boreal zone, except for sectt.Hecatonia/Xanthobatrachium, withR. hyperboreusandR. sceleratussubsp.reptabundus. Astonishingly few of the otherwise numerous lineages ofRanunculuswith distributions in the higher mountain systems of Eurasia and North America have acted as “founding sources” for the arctic flora. The only clear example is that of the arctic‐alpineR. glacialisand the BeringianR. chamissonisfrom the lineage of subg.R. sectt.Aconitifolii/Crymodes, although there might be others in sect.Auricomusnot recovered in the current molecular data. Lineages that gave rise to arctic taxa diverged from each other from the early Miocene (R. glacialis/R. chamissonis,Coptidium, lineages inHalerpestes) and continued at an even rate throughout the Tertiary. There are no signs that the intense climate changes of the late Pliocene and the Quaternary substantially accelerated or impeded diversification inRanunculus. Only the crown group split ofR. acrisand its relatives is clearly of Quaternary age. A detailed comparison concerning morphology, karyology, and life form excludes fundamental differences between taxa ofRanunculusin the Arctic and their respective closest relatives in regions south of it. Ecological traits, e.g., preferences for dry or moist soils or growth in open and sheltered conditions, also do not differ between arctic and nonarctic taxa. Migration into the Arctic